Rash on a human arm caused by contact with Poison Ivy (Toxicodendron (Rhus) radicans). This is a common source of contact dermatitis and allergic reaction caused by the substance toxicodendrol in the plant.

Other common poisonous plants that causes similar rashes include Poison Oak (Rhus diversilobum) and Poison Sumac (Rhus vernix). Some botanists used the generic name Toxicodendron.